1. Field of the Invention
The present invention relates to a process for manufacturing tyres for vehicle wheels.
The invention further relates to an apparatus for building a carcass structure of a tyre for vehicle wheels, said apparatus being usable in carrying out the above process.
2. Description of the Related Art
A tyre for vehicle wheel generally comprises a carcass structure comprising at least one carcass ply comprised of reinforcing cords embedded in an elastomeric matrix. The carcass ply has end edges respectively engaged with annular anchoring structures. The latter are arranged in the zones of the tyre usually identified with the name of “beads” and normally consist each of an annular substantially circumferential insert on which at least one filling insert is applied, in a radially outer position thereof. Such annular anchoring structures are commonly identified as “bead cores” and have the task of keeping the tyre well fixed to the anchoring seat specifically provided in the wheel rim, thus preventing, in operation, the radially inner end edge of the tyre coming out from such seat.
At the beads specific reinforcing structures may be provided having the function of improving the torque transmission to the tyre.
In a radially outer position with respect to the carcass ply, a belt structure comprising one or more belt layers is associated, said belt layers being arranged one on top of the other and having textile or metal reinforcing cords with crossed orientation and/or substantially parallel to the direction of circumferential extension of the tyre.
Between the carcass structure and the belt structure a layer of elastomeric material, known as “under-belt”, can be provided, said layer having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, made from elastomeric material as well.
Between the tread band and the belt structure a so-called “under-layer” of elastomeric material can be arranged, said layer having properties suitable to ensure a steady union of the tread band itself.
On the side surfaces of the carcass structure respective sidewalls of elastomeric material are also applied, each one extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
With particular reference to the zone of the tyre identified as “bead”, this is defined by a free end portion of the carcass ply specifically turned up and housing the annular anchoring structure or bead core and the filling insert therein. The coupling of the bead core to the carcass ply comprises in particular for a step prior to the step of turning up the free end portion of the carcass ply, wherein the filling insert of the bead core is brought into contact with the end edge of the carcass ply and a step simultaneous to the step of turning up-the free end portion of the carcass ply, wherein the filling insert of the bead core is laid down or pulled down on the end edge of the carcass ply.
U.S. Pat. No. 4,508,586 describes a process wherein turning up of the free end portion of the carcass ply and simultaneous pulling down of the filling insert of the bead core on the end edge of the carcass ply is carried out using an air tube specifically provided in an axially outer position with respect to the forming support on which the carcass ply is arranged. Such air tube, once inflated, raises the free end portion of the carcass ply so that this can be then turned up by the effect of the thrust action exerted on the inflated air tube by a special thrust member.
US 2005/0150587 A1 describes a process similar to the one discussed above, wherein a specifically designed and shaped air tube is used for turning up the free end portion of the carcass ply and simultaneously pulling down of the filling insert of the bead core on the end edge of the carcass ply, without the need of using any thrust member.
US 2006/0102272 A1 describes a process of the type discussed hereinabove, wherein in order to carry out the turning up of the free end portion of the carcass ply and the simultaneous pulling down of the filling insert of the bead core on the end edge of the carcass ply, a mechanical arm provided with pressing rolls at a free end thereof is used in place of an air tube.